1. Field of the Invention
The present invention relates to semiconductor wafer cleaning and, more particularly, to techniques for more efficiently cleaning wafer surfaces of interest and decreasing wafer cleaning cost.
2. Description of the Related Art
In the semiconductor chip fabrication process, it is well-known that there is a need to clean a wafer where a fabrication operation has been performed that leaves unwanted residues on the surfaces, edges, bevels, and notches of wafers. Examples of such a fabrication operation include plasma etching (e.g., tungsten etch back (WEB)) and chemical mechanical polishing (CMP). In CMP, a wafer is placed in a holder which pushes a wafer surface against a rolling conveyor belt. This conveyor belt uses a slurry which consists of chemicals and abrasive materials to cause the polishing. Unfortunately, this process tends to leave an accumulation of slurry particles and residues at the surface, edge, bevel, and notch of the wafer. If left on the wafer for subsequent fabrication operations, the unwanted residual material and particles may cause, among other things, defects such as scratches on the wafer surface and inappropriate interactions between metallization features. In some cases, such defects may cause devices on the wafer to become inoperable. In order to avoid the undue costs of discarding wafers having inoperable devices, it is therefore necessary to clean the wafer adequately yet efficiently after fabrication operations that leave unwanted residues.
One wafer cleaning method commonly employed is wet cleaning. In this method, a wafer which has undergone CMP is subjected to various cleaning chemicals. The cleaning chemicals have the effect of removing the slurry residues created by the CMP process. Unfortunately, such a cleaning method has been found to be less than adequate at cleaning the wafer edge, bevels or notches. Therefore, to adequately clean these areas, an extra step of edge cleaning may be required after the wet cleaning. An example edge clean method may be one described in U.S. Pat. No. 5,861,066, entitled Method and Apparatus for Cleaning Edges of Contaminated Substrates. This U.S. Patent is incorporated herein by reference. This U.S. Patent teaches a technique that employs rollers to clean the wafer edge during a brush scrubbing operation. This brush scrubbing operation would therefore be in addition to the wet chemical cleaning. Consequently, this extra step can have the effect of wasting time and increasing the cost of wafer processing.
In some cases, the top surface and the bottom surface of the wafer require treatment with separate chemicals. In order to accomplish this along with edge cleaning, three separate cleaning operations will be required. Furthermore, in some cases, the chemicals used for the cleaning of the top surface, for example, may cause unwanted reactions with chemicals used to clean the bottom surface. As can be appreciated, this level of cleaning can become quite complex and can have the downside of substantially slowing down wafer preparation.
In view of the foregoing, there is a need for a cleaning apparatus and process that avoid the problems of the prior art by allowing the simultaneous wet cleaning and edge cleaning of the wafer. Moreover, there is a further need for a cleaning device and process which allow the cleaning of the top surface, the bottom surface, and the edge of the wafer by separate methods simultaneously.
Broadly speaking, the present invention fills these needs by providing a cleaning system which simultaneously cleans the top surface, the bottom surface, and the edge of a wafer in one cleaning system. Although the detailed description describes many embodiments in relation to wafer cleaning, the term xe2x80x9ccleaningxe2x80x9d should be viewed broadly to include any type of wafer preparation, such as chemical cleaning, mechanical cleaning, brush scrubbing, or any combination thereof. For instance, wafers may, during processing, be exposed to the application or removal of films on the wafers or formed thereon. These films can include deposited films, thin films, spin-coated films, and the removal of those films using techniques such as etching and CMP. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, a system for use in semiconductor wafer cleaning operations is disclosed. The cleaning system has a top cap and a bottom cap. The top cap seals on a top surface contact ring of a wafer, and the bottom cap seals on a bottom surface contact ring of the wafer. The wafer is held between the top cap and the bottom cap. An edge clean roller is used for cleaning an edge of the wafer. A drive roller is configured to rotate the wafer, the top cap, and the bottom cap. The edge clean roller rotates at a first velocity and the drive roller rotates at a second velocity so as to facilitate an edge cleaning of the wafer by the edge clean roller.
In another embodiment, a system for use in semiconductor wafer cleaning operations is disclosed. The cleaning system has a top cap and a bottom cap. The top cap seals on a top surface contact ring of a wafer, and the bottom cap seals on a bottom surface contact ring of the wafer. The wafer is held between the top cap and the bottom cap. The bottom cap, the wafer, and the top cap are held stationary by a stand. The stand holds the bottom cap, the wafer, and the top cap stationary. The cleaning system also has an edge clean roller for cleaning an edge of the wafer. The edge clean roller rotates at a first velocity, and the edge clean roller moves around the wafer at a second velocity so as to facilitate an edge cleaning of the wafer by the edge clean roller.
In yet another embodiment, a system for use in semiconductor wafer cleaning operations is provided. The cleaning system has a top cap and a bottom cap. The top cap seals on a top surface contact ring of a wafer, and the bottom cap seals on a bottom surface contact ring of the wafer. The cleaning system also has an edge clean roller for cleaning an edge of the wafer. In this system, the bottom cap and the top cap rotate the wafer. The edge clean roller rotates at a first velocity and the wafer rotates at a second velocity so as to facilitate an edge cleaning of the wafer by the edge clean roller.
The advantages of the present invention are numerous. Most notably, by designing a cleaning system which cleans three different areas of a wafer simultaneously, wafer cleaning efficiency and throughput is improved. The claimed invention removes the problems of multiple cleaning steps and multiple cleaning machines which increases wafer cleaning costs and decreases wafer cleaning efficiency.
The present cleaning system can clean the top surface, the bottom surface, and the edge of the wafer simultaneously. Further, the present cleaning system can be contained in one housing so the wafer does not have to undergo multiple transportation steps which are frequent in traditional wet cleanings. Moreover, because multiple cleaning processes are carried out in one apparatus, the present cleaning system has good footprint utilization (takes up less floor space) which is very important for integrated systems used in the wafer fabrication. Therefore the present cleaning system will allow for more cost effective wafer cleaning and increased wafer cleaning efficiency.